1. Field of the Invention
The present invention relates to welding apparatus and systems, specifically Plasma Arc Welding ("PAW"), Tungsten Inert Gas ("TIG") and Metal Inert Gas ("MIG") arc welding systems. The invention relates particularly to arc welding systems of the type utilized for mechanized and robotic welding applications.
2. Description of the Prior Art
Typically, each of PAW, TIG and MIG arc welding systems includes a welding torch assembly in which a wire electrode is disposed through a current pick-up tip which applies welding potential to the electrode. The torch assembly includes a main body or housing to which is removably mounted a welding nozzle which surrounds the pick-up tip and channels an inert shielding gas to the welding arc. The nozzle may be air or water cooled. In PAW welding the nozzle also channels a plasma gas to the welding arc. The welding torch assembly must be serviced with the utilities which it requires for operation, such as water for cooling, gas for shielding the welding arc, plasma gas in the case of PAW welding, electricity to effect the welding, and, in the case of MIG welding, a consumable wire electrode. All of these utilities are fed to the welding torch assembly from associated supplies via utilities delivery means which may include a portable utilities station of the general type disclosed in my U.S. Pat. No. 4,210,796.
Water cooled nozzle assemblies for each of PAW, TIG and MIG welding have been provided heretofore, but in prior water cooled nozzles the cooling has been provided only to the exterior portions of the nozzle assembly. There has been no provision for directly cooling the pick-up tip assembly, which is typically insulated from the external portions of the nozzle. Thus, very high temperatures experienced by the pick-up tip assembly, which is typically of copper, can result in annealing of the copper and consequent shortening of the life of the tip assembly.
Certain water-cooled PAW welding torches, such as that sold by Linde Air Products Company under Model No. PT-8, provide the cooling water to the distal or working end of the nozzle and provide a threaded orifice insert which defines the plasma arc orifice and which cooperates with the working end of the nozzle to define a cooling water cavity or passage. For this purpose, O-ring seals are provided between the orifice insert and the nozzle body to prevent the escape of cooling water. However, the orifice insert must be screwed in a predetermined distance in order to properly engage the seals and the user cannot tell when the orifice has been turned in a sufficient amount. The extent to which the orifice insert is screwed in will affect the nature of the resulting plasma arc. Thus, it is difficult for the user to know when the orifice insert has been properly positioned for both effective sealing and optimal arc performance.
When prior arc welding systems are to be utilized in mechanized or automated applications, the welding torch assembly is fixedly mounted on the automated welding control equipment. For example, the welding torch assembly may be mounted on a permanent fixed mount to which workpieces are delivered for welding or, alternatively, may be mounted on a movable mount, such as that of a robotic welding machine, which moves to the workpiece under remote control, and which may be pre-programmed.
In such prior, arc welding systems, the replacement of the welding torch assembly or parts thereof is extremely inconvenient and costly, particularly in the automated or robotic applications, entailing a replacement of the complete assembly, including all of the utilities delivery means. Furthermore, in robotic welding applications, the replaced welding torch assembly will not be in precisely the same location and orientation with respect to the robot unit as was the original assembly, necessitating recalibration.
In order to alleviate these replacement difficulties, I have provided in my U.S. Pat. No. 4,600,824 a docking assembly for an arc welding system, which permits the welding torch assembly to be easily manually replaced at the welding station without affecting the utilities delivery means upstream of the welding station, and without losing the precise positioning of the torch assembly in the system.
There are many occasions when only the nozzle assembly needs to be replaced, and not the entire torch assembly. While removable nozzle assemblies have been known in the prior art, removal was not easy, particularly in the case of water-cooled nozzles, wherein replacement entailed shut down of the water supply at the source to avoid extensive water spillage at the welding station. Thus, I have also provided in my U.S. Pat. No. 4,582,979, a docking assembly which permits ready mounting and demounting of a water-cooled welding nozzle assembly at the welding station without spillage of cooling fluid.
While my above-described docking assemblies are usable in both TIG and MIG welding applications, they are not usable in PAW welding applications, since their docking bodies make no provision for the supply of a plasma gas in addition to a shielding gas. Heretofore, there has been no provision for providing simple manual replacement of a PAW welding nozzle at the welding station.
While there are similarities among PAW, TIG and MIG welding operations, there are also significant differences. Thus, in TIG and MIG welding, only a shielding gas need be supplied, while PAW welding requires not only a shielding gas but also a plasma gas. Furthermore, the systems require different electrode feeds, since in MIG welding a wire electrode is relatively rapidly consumed and must be continuously fed, while in TIG and PAW welding a tungsten electrode is essentially fixed, although it must be occasionally adjusted and/or the tip must be reground to repair slow erosion. Because of these and other differences, heretofore each of the three types of arc welding, viz., PAW, TIG and MIG, has required a completely separate welding torch assembly. However, it is frequently necessary for a single user to utilize, at different times at a given welding station, each of the three different types of arc welding. In such cases, it is necessary for the user to obtain three completely separate welding torch assemblies, viz., PAW, TIG, and MIG, each of which represents a substantial investment. Furthermore, switching from one type of welding to another necessitates replacement of an entire torch assembly and/or utilities delivery system at considerable cost in time and manpower.